ESTRO 2023 - Abstract Book

S1180

Digital Posters

ESTRO 2023

Materials and Methods 245 patients with PET/CT detected newly diagnosed metastatic prostate cancer were retrospectively reviewed. Patients with baseline PET/CT and bone scintigraphy were included. Images from baseline PET/CT and conventional imaging (low dose CT of PET and bone scintigraphy) were reviewed. Patients were sub-grouped into oligometastatic disease (OMD) and polymetastatic disease (PMD). OMD was defined as ≤ 5 bone and/or non-regional nodal metastases. Subgroup concordance was the same sub-group assigned for each modality. Results Between 2015 and 2021, 74/245 (30%) patients were analysed. 54/74 (73%), 9/74 (12%) and 11/74 (15%) patients had 68Ga PSMA-11, 18F PSMA-1007 and 18F-Choline PET/CT respectively. 50/74 (68%) patients had ISUP grade group 5, and 70/74 (95%) patients had ≥ T3 disease. Median age was 69 (range 48-86) years. Concordance for number of bone, nodal and visceral metastases is summarised in figure 1.

The total number of metastases detected with PET/CT was increased by 3-fold for bone metastases, and 2-fold for nodal metastases. 43/74 (58%) had bone metastases on bone scintigraphy, concordance for site was present in 39/43 (91%) patients. 35/74 (47%) patients had nodal metastases on conventional imaging, concordance for site was present in 33/35 (94%) patients. 38/74 (51%) patients were PET-OMD and 35/74 (47%) were PET-PMD, with a median PSA of 33 (range 3.2-400) ng/mL, and 61 (range 4.8-5400) ng/mL respectively. Concordance for OMD is summarised in figure 2.

In PET-PMD, 16/35 (46%) had 6-10 lesions and 12/35 (34%) had >10 lesions. In patients with 6-10 lesions, 10/16 (62) were OMD, and 5/16 (31%) were M0 on conventional imaging. In patients with > 10 lesions, 2/12 (17%) were PMD, 6/12 (50%) were OMD, and 4/12 (33%) were M0 on conventional imaging. 27/38 (71%) PET-OMD patients had prostate radiotherapy (± pelvic nodes, ± bone metastases). 18/35 (51%) PET-PMD patients had prostate radiotherapy (± pelvic nodes, ± bone metastases), all of which were “low-volume” on conventional imaging as per CHAARTED criteria. Conclusion PET/CT detects more metastases than conventional imaging. The magnitude of effect with a “right stage shift” poses implications on treatment decisions in the metastatic setting with potential overtreatment or undertreatment of patients. Work is on-going to expand the patient dataset to determine the patterns of response and relapse following PET/CT directed treatment.

PO-1458 Stereotactic focused radiotherapy for low-risk prostate cancer: results of a Phase-II trial

P. Nguyen 1,2 , B. Donneaux 2 , C. Louis 2 , S. Bodgal 2 , S. Philippi 2 , B. Frédérick 2 , S. Biver 2 , L. Harzé 2 , Y. Lasar 3 , G. Vogin 4 , P. Nickers 2,5 1 CHU UCL Namur - Site Sainte-Elisabeth, Radiotherapy, Namur, Belgium; 2 Centre François Baclesse, Radiotherapy, Esch sur-Alzette, Luxembourg; 3 Centre François Baclesse, Radiology, Esch-sur-Alzette, Luxembourg; 4 Centre François Baclesse, Radiotherapy, Luxembourg, Luxembourg; 5 CHU de Liège, Radiotherapy, Liège, Belgium

Purpose or Objective